1. Field of the Invention
The present invention relates generally to the field of illuminators, and more particularly to illuminators employed in the inspection of semiconductor wafers.
2. Description of the Related Art
Many optical systems provide an ability to inspect or image features on the surface of a specimen, such as inspecting defects on a semiconductor wafer or photomask. Certain advanced semiconductor defect inspection systems can detect defects on the order of 30 nm in size during a full inspection of a 300 mm diameter wafer.
The demands of the semiconductor industry for wafer and photomask inspection systems exhibiting high throughput and improvements in resolution are ongoing. Successive generations of such inspection systems tend to achieve higher resolution by illuminating the wafer or reticle using light energy having increased wavelength and power. Highly detailed inspection can benefit from broadband illumination having high average power coherent radiation. Further, operation in the wavelength range of substantially 150 nm to 500 nm can be beneficial in current wafer inspection arrangements.
Previous illuminator designs tend to offer limited brightness levels as measured in terms of watts/cm2-str-nm. Previous designs for high power broadband illumination include mercury xenon lamps having power in the range of 500 watts to 1000 watts, as well as brightness of approximately a few hundred W/cm2-str in the integrated wavelength range of 150 nm to 500 nm. Proposals have been made to use cascaded arc lamp arrangements, thus providing brightness of roughly a few kw/cm2-str in the integrated wavelength range from 150 nm to 500 nm.
Use of mercury xenon or cascaded arc lamps tends to be limited in that when used with very small sensor pixels and apertured illumination modes, they can be unable to be imaged with sufficient intensity to enable adequate operation of TDI sensors. Efficient light use in the presence of relatively small pixel sizes requires focusing to match the radiation footprint to the sensor image area at the wafer plane. Mercury xenon and cascaded arc lamps tend to be limited in the average power at the wafer plane for small sensor pixels due to their limited brightness, particularly in imaging modes such as edge contrast, where as the name implies, the contrast of the edge of the wafer is examined and illumination and collection employ apertures to emphasize edge scatter. Edge contrast modes and similar illumination modes tend to waste illumination radiation, and thus limit the average power available for inspection.
In the semiconductor inspection environment, an illuminator or illuminating arrangement transmitting light with a high average power and brightness may provide benefits over previous types of illuminators. Such an illuminating arrangement operating at sufficient average power and brightness levels that can successfully operate in the presence of TDI sensors and using an edge contrast mode may be preferable to other previous types of illuminators depending on the application. Further, such an illuminator design that does not damage the wafer would be highly beneficial.
It would be beneficial to provide a system overcoming these drawbacks present in previously known systems and provide an optical inspection system illumination design having improved functionality over devices exhibiting those negative aspects described herein.